This invention relates generally to accurate determinations of position, and more specifically to, integration of global positioning satellite (GPS) units and inertial navigation systems (INS) units with remote velocity sensors (RVS).
Known integrated GPS/INS units are capable of providing accurate position, velocity, attitude, and acceleration data, either through a user interface or as data that is communicated to another control system. However, transforming such data to points on a vehicle a distance away from the GPS/INS units, for example, at a location of the GPS antenna, can result in an unacceptably large position, velocity, and acceleration noise. The noise results due to the effect of the distance between a sensor of the INS, at a first point on the vehicle, and the point of interest, at a second point on a vehicle.
Accurate determinations of velocity and acceleration for different points on a vehicle are needed to aid in operation of GPS tracking loops and synthetic aperture radars. A purpose for a remote velocity sensor is to provide accurate acceleration, velocity, and position data at any point in a vehicle, and providing such data at a low noise level.
In one aspect, a unit configured to provide acceleration, velocity, and position information for one or more points on a vehicle is provided. The unit comprises an integrated global positioning satellite system (GPS)/inertial navigation system (INS) and at least one remote velocity sensor. The remote velocity sensors comprise three orthogonal accelerometers and a digital signal processor configured to receive signals from the accelerometers. The remote velocity sensors are mounted at points on the vehicle where acceleration, velocity and position are to be determined. Data from the sensors is slaved to data from the integrated GPS/INS, and the unit is configured to transform data from the sensors to a navigation frame utilizing a sensor frame to navigation frame attitude matrix.
In another aspect a method for removing a low frequency drift in data from a remote velocity sensor is provided. The remote velocity sensor includes a digital signal processor (DSP) and three orthogonal accelerometers which provide signals to the DSP which generates the data. The remote velocity sensor is configured for communication with an integrated GPS/INS. The provided method comprises receiving data from the remote velocity sensor, receiving data from the integrated GPS/INS, and transforming the data from the remote velocity sensor to the data from the integrated GPS/INS using a sensor frame to navigation frame attitude matrix.
In still another aspect, a filter is provided which is configured to receive GPS/INS position, velocity, and attitude data and remote velocity sensor (RVS) position and velocity data. The filter separately integrates both GPS/INS velocity and RVS velocity over a filter period. A difference between the RVS velocity integration and the GPS/INS integration is formed and a RVS velocity solution is corrected based on the difference.